Local police said that the activists were detained in the early hours of September 12 after they refused to leave a bus parked near the central square in the regional capital, Ulan-Ude, where they spent the night before resuming their protest after sunrise.

According to the police, law enforcement officers began detaining the activists after they threw a tear-gas grenade towards the police.

Meanwhile, correspondents of the Moscow-based Novaya Gazeta newspaper reported that it was police who threw a tear-gas grenade inside the bus to force the activists, including a pregnant woman, to leave the vehicle.

The city administration said on September 12 that it received a letter from an unidentified individual that threatened to set off a series of explosions in public areas unless all of the detained activists were released and a new mayoral election held.

Protesters began gathering on the central square in Ulan-Ude on September 9 to demand a revision of the results of the election held a day earlier for the city's mayor and expressing their support for a shaman, Aleksandr Gabyshev, who has been walking from the Far Eastern region of Sakha-Yakutia for four months to Moscow "to drive President Vladimir Putin out of the Kremlin."

The protesters say the election was rigged to secure the victory of an independent candidate and acting Mayor Igor Shutenkov.

Shutenkov's main competitor, Vyacheslav Markhayev of the Communist Party, called the election "the most devious and dirty among all of those I have taken part in."

On September 10, police detained local lawmaker Bair Tsyrenov of the Communist Party and activist Dmitry Bairov, who were among the protesters.

Tsyrenov was later fined 15,000 rubles ($230) for taking part in an unsanctioned rally and Bairov sentenced to five days in jail on the same charge.